1. Field of the Invention
The present invention relates to a solid-state image sensor and a camera including the same.
2. Description of the Related Art
As the number of pixels of a solid-state image sensor increases, the size of the pixel decreases, and the area of a photoelectric converter decreases accordingly. Generally, the sensitivity of a pixel decreases as the area of a photoelectric converter decreases. Japanese Patent Laid-Open No. 2008-042238 has disclosed a technique that increases the sensitivity by causing a plurality of pixels to share a transistor and floating diffusion, thereby decreasing the ratio of the area occupied by these components, and suppressing the reduction in area of a photoelectric converter.
Japanese Patent Laid-Open No. 2005-109411 has disclosed a structure that reduces the decrease in sensitivity caused by the reduction in area of a photoelectric converter. This structure is called a light waveguide, and can be formed by forming a hole in a planarization film above a photoelectric converter, and filling a high-refractive-index material in the hole.
Generally, a spatially localized electromagnetic wave has the property of spreading by diffraction. The light waveguide propagates light by returning light that travels away from the optical axis toward the optical axis by reflection and refraction, and thus confines it inside the waveguide along the optical axis. Therefore, the light waveguide can efficiently guide light incident on its upper portion to a photoelectric converter. However, the light incident on the upper portion of the light waveguide is not entirely guided to the photoelectric converter, and some light leaks out of the light waveguide.
In a solid-state image sensor in which a plurality of pixels share a floating diffusion, the structures of the pixels sharing the floating diffusion can be different from each other. Assume that a first pixel has a polysilicon pattern outside a light waveguide, and a second pixel has no polysilicon pattern outside the light waveguide. In this case, in the first pixel, light leaking out of the light waveguide may be incident on the polysilicon pattern and reflected or refracted. In the second pixel, however, no such phenomenon caused by the polysilicon pattern occurs. This produces a sensitivity difference between the first and second pixels. A sensitivity difference like this may produce fixed pattern noise in an image.